The IEEE 802.15.4 standard [1] has emerged as a strong technology for Wireless Sensor Networks (WSNs) to morph Personal Area Networks (PANs) into Low power Wireless Personal Area Networks (LoWPANs). LoWPANs are characterized by low data rates, low power consumption, low costs, autonomous operations, and flexible topologies. In order to fully realize a pervasive or ubiquitous environment, LoWPANs must be connected to the Internet. Internet Engineering Task Force (IETF) is standardizing the transmission of IPv6 over LoWPANs through 6lowpan (IPv6 over Low power Wireless Personal Area Networks) working group [2]. The emerging application range of 6LoWPAN includes consumer appliances, home automation, monitoring and control in industrial environments, military, and environmental monitoring, etc.
Incorporating mobility in 6LoWPAN [3] can lead to the realization of new and exciting applications. For example, mobility of 6LoWPAN devices can be exploited in health care applications. In this case, the patients have sensor nodes embedded in their clothes for sensing some of their important health parameters like pulse rate and temperature, etc. These sensor nodes can sense the data and transmit it to a monitoring facility, even when the patient is moving, by using one of the existing communication technologies like WLAN and UWB. However, these technologies are more applicable when the application requires high data rate and often demand complex link and physical layer solutions with complicated hardware. 6LoWPAN has been considered as the most suitable technology for supporting mobility in sensor networks due to their low power and low data rate characteristics. Also, 6LoWPAN enables the integration of IEEE802.15.4 networks with the Internet, thereby increasing the monitoring scope of the patient.
In order to prevent packet losses due to mobility, some of the existing tunnel-based mobility protocols like HMIPv6 [4], FMIPv6 [5], and MIPv6 [5] can be used. These schemes can help a Mobile Node (MN) to maintain its ongoing communication with the outer world and to minimize the packet losses while it is moving. However, the above mentioned schemes are host-based mobility protocols in which the MN actively participates in mobility-related signaling. Moreover, these are network layer solutions that provide mobility-related features at the IP layer. In other words, mobility-related packets are carried by the IP traffic [6]. Similarly, routing-based mobility management schemes like HAWAII [7] and Cellular IP [5] require the MN to manage its mobility by sending path-setup messages and periodic path-refresh messages [7]. Also, in HAWAII, the domain router could become a potential bottleneck, as all of the MN's packets are routed through it. Another mobility support protocol is NEMO that requires a mobile router (MR) to support the mobility of a PAN [8].
PMIPv6 [9] is a network-based mobility support protocol currently being standardized by IETF's netlmm (Network-based localized mobility management protocol) working group. PMIPv6 could be considered as a suitable candidate to enable mobility in 6LoWPAN devices, as in the scheme the network handles all the mobility-related signaling on behalf of MNs. However, at its current phase, PMIPv6 defines the interface between the Mobile Access Gateway (MAG) and a MN for one-hop communication at the network layer. It does not specify the interface between MN and MAG for multi-hop communication. Also the mobility-related packets exchanged between network entities are carried by IP traffic. Moreover, PMIPv6 demands another level of tunneling overhead at the network layer between the Gateway (GW) and the MAG that serves MNs.